During charging of a battery, e.g., a lithium ion battery, total voltage at the battery pack may increase sharply due to increasing overvoltage at certain laminating parts at which degradation has occurred. Thereby, total voltage reaches an upper bound voltage, which is set in order to prevent overcharging, and the charging system stops charging considering that the battery pack is fully charged.
However, as degradation of the battery progresses the battery pack is typically not yet fully charged (i.e., state of charge (SOC)<100%) when charging is stopped as a result of reaching the upper bound voltage. Therefore, available amount of energy from the battery decreases due to the degradation dispersion.
US 2004/0096749 is directed to preventing overcharging a all laminating parts of a battery using a characteristic charging capacity rate, which remains substantially unchanged until SOC approaches 100%. However, US 2004/0096749 does not take into consideration the influence of overvoltage when the battery has degraded due to use. In addition, the techniques disclosed therein require the implementation of special materials.